The present invention relates to an exhaust pipe of an internal-engine, having at least one catalyst in the exhaust pipe and at least one adjustable throttle element in the exhaust pipe.
From the German Patent Document DE-OS 23 21 578, a throttle element made of bimetal for the exhaust pipe of an internal-combustion engine is known which, when the exhaust gas temperature is low, opens up the full cross-section of an exhaust gas pipe and, when the temperatures are higher, swivels a damming element into the exhaust gas flow. By means of this arrangement, a faster heating of the core zone of the catalyst after the start of the internal-combustion engine is achieved as well as a uniform durability-increasing action on the catalyst after it has reached its working temperature.
An object of the invention is to provide an exhaust pipe of an internal-combustion engine comprising a catalyst in which the catalyst, after the starting of the internal-combustion engine, reaches its working temperature as fast as possible.
This and other objects are achieved by the present invention which provides an exhaust pipe of an internal-combustion engine. This exhaust pipe includes at least one catalyst arranged in the exhaust pipe and one adjustable throttle element arranged in this exhaust pipe. The throttle element has an upstream stationary end adjacent to a first side wall of the exhaust pipe, and a downstream, movable end. The throttle element is positioned such that when the internal-combustion engine is cold, the movable end forms a gap with a second side wall opposite to the first side wall.
By arranging a throttle element in the exhaust pipe which, when the internal-combustion engine is cold, reduces the cross-section of the exhaust pipe down to a residual gap, the exhaust back pressure is increased. For compensating this increased back pressure, the mass flow rate of the engine is increased, whereby the exhaust gas temperature rises and the catalyst reaches its working temperature faster. The throttle element may be constructed as a bimetal or a memory metal and, with its upstream stationary end, is arranged adjacent to a side wall of the exhaust pipe. In the cold condition, the downstream free end forms a gap with the opposite side wall. In the cold state, the throttle element thus blocks the exhaust pipe down to the gap required for the flowing-off of the exhaust gas quantity occurring in the cold start phase. As the internal-combustion engine warms up, the exhaust gas temperature increases, whereby the throttle element deforms and in this case progressively opens up the whole cross-section of the exhaust pipe. The elasticity of the throttle element is designed such that, in the case of a cold start and an immediate high load, the exhaust gas flow lifts the throttle element thus enlarging the gap.
Advantageously, the arrangement of the present invention is self-regulating so that no sensors or control elements are required. It has a simple maintenance-free construction and is preferably arranged downstream of the catalyst, whereby the catalyst is warmed up in an optimally short time.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.